In order to determine a marker of prethrombotic states, reliable and easy to measure, we studied 200 patients under 60 years of age admitted to hospital for a precordial chest pain. Four groups were established: transmural myocardial infarction, acute infarction without Q wave, unstable angina and atypical chest pain. Fibrinogen, von Willebrand factor, cholesterol, and triglyceride levels were measured as well as the white cell and platelet counts. There was a statistically significant correlation between transmural myocardial infarction and increased levels of fibrinogen, von Willebrand factor and white blood cells. Von Willebrand factor was already increased in the acute phase of transmural infarction, reached a maximum on the fifth day and then decreased slowly during the following ten days. This study suggests that plasma von Willebrand factor could be a reliable marker of transmural myocardial infarction in the acute phase or during the two weeks following the thrombotic event.